Roadside Passive MASW for Limestone Bedrock Characterization and Urban Infrastructure Planning in Cam Pha, Quang Ninh Province

Abstract

Characterizing shallow bedrock beneath urban corridors is important for infrastructure planning in limestone terrain, where irregular rockhead geometry can complicate foundation and excavation design. This study evaluates roadside passive multichannel analysis of surface waves (MASW) as a low-disturbance approach to ground assessment along a 141 m road corridor in Cam Pha, northeastern Vietnam. Traffic-induced surface waves were recorded at four array positions using twenty-four 4.5 Hz geophones spaced 3 m apart. At each position, dispersion images from ten 32 s records were stacked, and selected dispersion curves were inverted to obtain one-dimensional shear-wave velocity (VS) profiles. An interpolated two-dimensional section was compared with stratigraphy from a nearby borehole. The models extended to approximately 50 m depth and indicated clayey cover with VS mostly around 270–400 m/s overlying limestone with velocities commonly exceeding 1500 m/s. The interpreted clay–limestone boundary generally occurred at 15–20 m depth, with local deepening near the middle of the section. Depth-averaged velocities over the upper 30 m ranged from 434.24 to 497.63 m/s, corresponding to NEHRP site class C and Eurocode 8 ground type B. The findings support preliminary ground assessment and prioritization of confirmatory investigations for urban infrastructure. However, the interpolated section and single borehole do not uniquely resolve the causes of local bedrock irregularities; additional investigations are needed before site-specific design decisions.